usfmarine
Non-Com
SJA, Scooter Rebellion
Posts: 74
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Post by usfmarine on Dec 5, 2009 18:51:56 GMT -5
Hey Doug, after we cleaned up our head/cylinder mating surfaces with sandpaper at your house, I read that we should not have done that since we were probably taking off a lot more aluminum than we thought(and removing it very unevenly most likely). Your oil leak could be caused by the uneven cylinder or head surfaces. Just throwing ideas out there since I know how annoying oil leaks are. Next time I take apart the engine, I am going to have a piece of glass or something very flat in order to evenly smooth my head and cylinder. Just a thought...
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Post by Rebel on Dec 6, 2009 2:21:36 GMT -5
I've never sanded on aluminum, I have used a buffing wheel on iron and had no problem, but then a buffing wheel is not as abrasive as sandpaper. I still think that if it is running well you probably didn't hurt the head surface, had you done that you would be blowing the head gasket. It is still possible you caught the outer edge of a oil channel and sanded it down too much I guess.
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Post by Doug in San Diego on Dec 6, 2009 10:20:22 GMT -5
I agree.
I didn't go crazy with the sandpaper. I just lightly took off the black gunk.
I suspect the leak is at the bottom cylinder gasket (I did not replace the bottom gasket this time)
Do they make a "stop leak" oil additive?
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Post by kuzikood on Dec 6, 2009 11:26:36 GMT -5
i wouldnt use a stop leak it gums things up wayyyyyyyyy too much its only a last resort on a engine thats gonna die anyway to get a couple more months out of it before ya run it over the scales
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Post by Rebel on Dec 6, 2009 11:33:52 GMT -5
Stop leak, I agree with Kuzikood on that one.
If you were going to re-use that bottom gasket it would have been best to use silicone on both sides, or no gasket and then a bead of silicone in its place. IMO
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Post by Doug in San Diego on Dec 7, 2009 0:44:33 GMT -5
So let me ask
If you change the CAM (remove head 4 head nuts and head) do you need to pull off the cylinder and replace the bottom gasket too?
We did not do that. I did replaced the bottom gasket when I put in the new piston
I still feel like I am missing some trick to this . After doing it a few times, I'm not worried about the mechanic part, but I would like to get it done right for once. There must be something Im missing (better gasket, simple tip, I dunno)
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Post by Rebel on Dec 7, 2009 0:58:22 GMT -5
if you didn't break the bottom gasket loose, you do not need to replace it, at least I wouldn't. I'd check for a leak at the valve cover gasket. On a simple cam change the head does not need to come off.
When you are tightening the bolts down, what kind of sequence are you using?
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Post by kliff on Dec 7, 2009 7:25:19 GMT -5
Like Doug said, if you didn't break the gasket loose...problem is, are you sure you didn't break it loose? I hate re-doing work, that was preventable. If I pull the head, I pull the cylinder, and replace both gaskets. How much does a base gasket cost? How long to clean the surfaces of block and cylinder.... $7.00 & 45 minutes.
What's a re-doo, that $7.00 + 45minutes, lus another head gasket, possible intake and exhaust gasket, and another 5-6 HOURS. I just do it the first time, and write it off to preventative Maintenance.
Didn't I mention gasket cleaning with single edge razor baldes? NEVER clean aluminum sealing surfaces with sandpaper, and certainly not with anything like 150. Unless you have PLATE GLASS minimum, or a machinists MARBLE plate, never get close to a machined aluminum surface with anything coarser than 600, and finish that with 1200 grit, both kept wet with WD-40, never allowed to dry out. If you have the coin, just spring for a 24" lapping block: cast iron, FLAT, with machined grooves to retain lapping compound.
But don't sit down and sand the gasket offf....just don't do that.... that's the kinda work mud farmers do. NOT aspiring engine builders.
You guys wonder why I'm short temperred sometimes.... I sit down, and lay out step by step, what to do, what to use, to do it, then when you deviate, and problems arise.....
I'll bet ya some of those mud farmers will even tell you how to surface mill the head with an 80grit disc in a 12" side grinder.....how to grind valve faces with a 1/4" drill... how to open up a set of cases with a dremel for larger bore jug.... which "stones" to use when grinding aluminum....
I try to keep my stuff as "low buck" for y'all as possible, but I'm not gonna piss down your back, and tell you it raining neither.
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Post by Rebel on Dec 7, 2009 12:46:35 GMT -5
LOL, Kliff, give 'em hell.
Well I know this, once a mistake is made, a lesson is learned. So those of you that are learning yes you will make some errors and learn some lessons, have to redo a job once or twice. The good thing is this, you learn AND the price of parts on these GY6 scooters is cheap enough they shouldn't break the bank. Also, most of us that didn't have a person to work along side of us and make fun of us as we did something under the level of genius most certainly had some of the same embarrassments. Like I said, I never sand aluminum.
Dremel on cases for a big bore kit. I remember on another forum a long time back where that was the accepted method to open a case up, no cleaning out the shavings and grit or anything, then about a year , or a little longer back. I mentioned that that method didn't really sit well with me and my way of thinking. All of a sudden another voice cried out too, no that ain't the right way to do it, finally a confirmation of sanity I thought, it was Kliff and a new way of doing things the right way was finally being voiced, Kliff does do things by the book, the way you would get it done from a professional mechanic, so he does give out the proper advice and if you want to do it the right way just print off a copy of what he says and take it out to the job site, garage, kitchen where ever and refer back to it.
Still, if it is holding compression, I doubt you messed the head up, just don't do it again.
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Post by kliff on Dec 7, 2009 16:26:38 GMT -5
STOP LEAK!
I ain't even going there.... kuzikood and Doug done jumped you, on that, I ain't gonna kick ya while you're down....LOL
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Post by Rebel on Dec 7, 2009 17:37:42 GMT -5
Back on my question about tightening the head bolts down. If you do both of them on one side at a time it is possible to have a problem with it sealing well. Heads should be tightened and then torqued down so that it comes as straight as possible down. with these you only have four bolts you should go from one corner to the other side and the opposite end of the head, caddy corner, then go on the second side you did to the other corner rand finally just below or above the first one you tightened down, then you are ready to torque it using the same kind of pattern for torquing them.
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usfmarine
Non-Com
SJA, Scooter Rebellion
Posts: 74
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Post by usfmarine on Dec 7, 2009 20:07:24 GMT -5
Back on my question about tightening the head bolts down. If you do both of them on one side at a time it is possible to have a problem with it sealing well. Heads should be tightened and then torqued down so that it comes as straight as possible down. with these you only have four bolts you should go from one corner to the other side and the opposite end of the head, caddy corner, then go on the second side you did to the other corner rand finally just below or above the first one you tightened down, then you are ready to torque it using the same kind of pattern for torquing them. That's good advice. I did see Doug tighten his down in that manner. I wonder what's causing his leak...
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Post by Rebel on Dec 7, 2009 22:54:08 GMT -5
I'll admit, I've put motors back together, did everything as close to the book as I could and still had a leak, then had to take it apart and put a new gasket in to fix it. First thing you should do though is figure out where it is coming out of. Clean the motor as clean as possible, then run it to see the leak.
Doug, if you take that head off, go back to the post where Kliff spoke about a machinist rule, go buy one and then use it on every angle you can think of to check it for being flat and having no low spots, alternatively get a half inch think 12X12 piece of glass and lay that head on top of it and see if there is any imperfection you can see. if you see a place where you sanded it down you'll need to get the head milled at a machine shop to fix it.
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Post by Rebel on Dec 14, 2009 1:56:13 GMT -5
FYI, here is a picture of a pair of new valves for a 150cc GY6 actually what they are for makes no difference because all stock valves look alike. Notice the shiny mating surface on the edge of the head of it, that is what they are supposed to look like at all times, the rusty pitted picture that was posted earlier in this thread shows what it should not look like.
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Post by Doug in San Diego on Dec 14, 2009 23:22:42 GMT -5
Sorry for the delay on a solution guys
Between damn kids (I am a teacher and I now hate homerwork - 3 hrs plus crying today)
Wife - Who schedules a Christmas party in the middle of a Charger game???!!!! - Still I went!
and rain
I have had zero time for the scoot. I did buy a $15 compression tester from Harbor Freight though. My pressure was a solid 150. Now I know my rings are not blowing back
Anyway, I will have more time after Thursday to re-torque the head bolts, and try to find the leak.
As always I recognize my half-assedness always bites me in the butt.
I'll keep y'all posted.
Doug
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